MEMS free-space optical switches can be categorized into two major branches: the planar matrix (2-dimensional) approach, and the beam-steering (3-dimensional) approach. The 2D approach typically involves mirrors that move between on and off position. The angular accuracy at the on position is extremely critical as it affects the alignment of the mirror and optical loss of the switch.
Using <110> silicon with anisotropic etchants, one can form trenches with 90-degree sidewalls. If one bonds this wafer to another wafer that has free rotating mirrors, the sidewall can serve as a reference stopping plane to fix the up- mirrors in a vertical position. In addition, the sidewall may also serve as an electrode for electrostatically clamping the mirror in the vertical position.
One type of optical switch employs microelectromechanically-actuated mirrors. FIG. 1 depicts one type of MEMS actuated switch 100 that is made using 2 substrates. A top chip 101 containing a sidewall for receiving a movable mirror 111 is bonded to a bottom chip 102 containing a base 103. There are a few complications associated with the two-wafer approach. The attachment process requires a very high accuracy aligner-bonder. Moreover, the two-chip process places certain geometrical constraints that limit the minimum geometry of the trenches and mirrors. Furthermore, the complexity of the fabrication and alignment process can increase cost and reduce yield.
Therefore, there is a need in the art for a low-cost, high-yield scalable switch and a process of fabricating same.